Your flash has an Auto mode that you can use with your 501CM for fill flash.
Set your camera to the shutter and aperture desired and metered.
On your flash set the film speed then set the dial to one of the auto exposure apertures that is 1 or 2 stops larger than metered and seton the camera. In other words if you measured and set the aperture on the camera at f11 then set the flash to f8 or f5.6 depending on how much fill you desire. You need to assure the subject distance falls in the aperture you set on the flash otherwise choose a different shutter/aperture combination and set the aperture on the flash accordingly that gives you the range.

It sounds more complicated than it is.

Do you have a manual for our flash?

You can find one here...

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